Method and apparatus for highline tension control



June 1968 E. H. BORN ETAL METHOD AND APPARATUS FOR HIGHLINE TENSIONCONTROL Sheets-Sheet 1 June 11, 1968 E. H. BORN ET AL. 3,388,070

METHOD AND APPARATUS FOR HIGHLINE TENSION CONTROL Filed Feb. 25, 1967SHIP SEPARATION 2 Sheets-Sheet 2 I A L. BS98 3 Q L E'LQ L SHIP CLOSUREATED WINCH OPER TO PAY OU CABLE SHIP SEPARATION SHIP CLOSUREHYPOTHETICALRAM TENSION"\\\ osmou IF NO CORRECTION I [OR RA TE OFPOSITION CHANQE Rm "T'EIEIENEFF afizioinm:

POSITION SHIP ROLL RAM TENSIONER RESULTING FROM HYPOTHETICAL UNCORRECTEDFOR POSITION INVENTORS fi %5M 3 @W sesame METHOD AND APPARATUS FORHiGHLINE TENSlGN QUNTBQL Ellis H. Born, Qolumhus, Peter B. Burnharn,Worthington, and Paul Wolfe, Dublin, @hio, assignors to AhexQorporation, New York, Fifth, a corporation of DelawareContinuation-lament of application Ser. No. 496,4tl8,

Get. :5, W65. This application Feb. 23, 15 67, Ser.

11 Claims. (Cl. 254-172) ABSTRACT (BE THE DHSELUSURE A method andapparatus for automatically and continuously maintaining a presettension on the highline of a transfer system for transferring articlesbetween two moving ships at sea.

Cross references to related application This application is acontinuation-in-part of copending application Ser. No. 486,408, filedOct. 15, 1965.

Brief summary of the invention In the transfer of articles between twomoving ships at sea, it is customary to utilize one cable or so-calledhighline extending between the two ships to support a trolley whilesimultaneausly another cable or so called transfer line is used tocontrol movement of the trolley over the highline. In our copendingapplication Ser. No. 496,408, we have disclosed a completely automaticsystem for controlling the transfer cable during transfer or the trolleybetween the ships. The invention of this application concerns automaticcontrol of the highline so that cable is payed out or taken in asrequired by the relative movements of the ships.

A highline cable normally extends from a cable winch on the supply ship,through a multiple wrap ram tensioner and over to the receiver slip towhich it is attached. The ram tensioner comprises a multiple wrap blockand tackle having one fixed pulley spaced from a second movable pulley,the two pulleys being biased apart by a spring or compressible element.Because of the several wraps, the ram holds approximately seventy feetof cable in reserve and available in the event that the ships separateby that distance or move together to that extent. This is suflicientcapacity to handle normal roll and pitch of the two ships in relativelyrough seas. However, if the ships should take diverging or convergingcourses, or if the ships should roll excessively, this capacity isinsufficient and cable must be stripped from or taken in by the winch tocompensate for these relative movements. Prior to this invention, thispaying in or out of cable from the winches has always been handled by aseaman who watched the tensioning ram and when he thought it was tootight, caused the winch to pay out line, and when too slack, caused itto take in line. This method is at best haphazard and often resulted inbroken and lost cable and trolleys.

This invention is predicated upon the concept of automaticallycontrolling operation of the highline winch by monitoring the positionof the ram tensioner which is a function of the tension of the cable andutilizing the monitored information to control the winch. In thepreferred embodiment, the monitored information is converted into anelectrical signal, the amplitude of which is a function of the ramtensioner position. This electrical signal is passed through a deadbandfiltering circuit operative to pass only signals of predeterminedamplitude so States Patent 0 3,388,7 Patented June 11, 1968 that huntingor constant operation of the winch is avoided. From the filteringcircuit, the signal is fed as an input into three parallel controlcircuits; a signal duration damping circuit, a very high positionoveride control circuit, and a position rate of change override controlcircuit. A signal passed by any of these three parallel circuits becomesa command signal to a servo control valve which in turn controlsoperation of a fluid pump and motor system operative to drive thehighline winch.

The signal duration damping circuit functions to pass a command signalwhenever it has persisted for a preset time interval, as for example 7/2 seconds. This is approximately one-half of the normal roll cycle timefor a supply ship so that this circuit operates to dampen out allsignals resulting from the roll and pitch of the ships which can behandled without winch operation by the tensioning ram. If the shipsshould change to a diverging or converging course, this control circuitwill pass a correction or a command signal to the servo control systemafter the signal has persisted for the preset time.

The position overide control circuit and the rate of position changeoverride control circuits both function to protect the system againsthigh rate, long duration cable tension and ram tensioner positionchanges which could break the cable or cause an accident if thecondition persisted for the time interval required to operate the signalduration dampening circuit. The position override contol circuitcomprises an amplitude discriminating circuit operative to pass only asignal indicating an unusually high or low ram tensioner position. Therate of change circuit measures the rate at which the ram tensionerposition is changing and if excessive, passes a command signal to thewinch control servo to immediately initiate operation of the winch.

The primary advantage of this highline control system is that itautomatically controls highline tensioning while permitting the ramtensioner to handle the high frequency and low amplitude positionchanges. In this way wear and tear of the winch and winch controlsystem, as well as power consumption is minimized.

These and other objects and advantages of this invention will becomemore readily apparent from the following description of the drawings inwhich:

FIGURE 1 is a diagrammatic illustration of a highline transfer systemfor transporting articles between a supply ship and a receiver ship,

FIGURE 2 is an electric-hydraulic diagrammatic illustration of theinventive highline winch control circuit of this application,

FIGURE 3 is a graph on which relative ship positions are plotted on areference line basis, the solid sine wave illustrating a normal maximumship roll rate and ampliplitude and two dashed output curvesrepresenting input and output to the integration control circuit,

FIGURE 4 is a graph on which relative ship positions are plotted on areference line basis, the solid sine wave illustrating a normal maximumship roll rate and ampli plitude and the two dashed curves representinguncorrected and corrected positions of the ram tensioner resulting fromexcessive rate of ram tensioner position change,

FIGURE 5 is a graph on which relative ship positions are plotted on areference line basis, the solid sine wave form illustrating a normalnon-sine wave rate and amplitude and the two dashed curves representinguncorrected and corrected high amplitude ram tensioner position.

Referring first to FIGURE 1, there is diagrammatically illustrated aconventional highline transfer system for conveying a trolley it)between a supply ship 11 and a receiver ship 12. This is just one ofseveral difierent systems or methods of transferring articles betweenships but is the one conventionally used whenever heavy loads are to betransferred. In accordance with this method, the trolley is suspendedfrom and rolled over a highline 14 while a transfer cable 15 attached tothe trolley 10 is payed out or taken in so as to maneuver the trolleybetween the ships. Conventionally, the transfer cable 15 extends from aninhaul winch 13 on the supply ship, over a pulley 16 on the supply ship,to a point of attachment 17 with the trolley. From the attachment point17, the transfer cable 15 extends to and around a pulley 18 on thereceiver ship, and back to an outhaul winch 19 on the supply ship. Byproperly maneuvering the inhaul and outhaul winches 13, 19 to pay outcable from one winch and take it in on the other, the trolley 10 may beconveyed between the ships. A completely automatic system forcontrolling the inhaul and outhaul winches so as to effect automatictransfer of the trolley between the ships is disclosed in our co-pendingapplication Ser. No. 496,408.

The invention of this application concerns the automatic operation ofthe highline winch 20 so as to pay out or take in cable as required bythe relative movements of ships as they are moved apart to together as aconsequence of roll, pitch, yaw or varying courses between the twoships.

When completely rigged, the highline 14 extends from a drum of thehighline winch 2d, beneath an idler pulley 29, through a tensioning ram21, beneath another idler pulley 28, over a pulley 22, to a point ofattachment 23 on the receiver ship. A pair of freely rotatable rollersor pulleys 24 attached to the trolley 10 ride over the highline 14, andsupport the weight of the trolley 1% from the highline.

The ram tensioner 21 is a conventional piece of nautical equipment andhas, therefore, not been illustrated in detail. It comprises astationary frame 39 upon which is rotatably mounted a multiple Wrappulley 31 and a vertically movable and rotatable multiple wrap pulley32. Generally, both pulleys 31, 32 support three wraps of cable so thatthe cable and pulleys 31, 32 act as a large block and tackle between thewinch 20 and pulley 22.

Generally a hydraulic motor 34; (FIGURE 2) in cooperation with an airaccumulator 35 biases the movable pulley 32 away from the stationarypulley 31. The cylinder 37 of motor 34 contains a fluid reservoir 38beneath a piston 36 so that when the piston is forced down by thetension in the cable, fluid is forced from the reservoir into the airaccumulator 35. Air entrapped in this accumulator is thereby compressedso that it acts as a large compression spring. Of course, a large metalspring could be substituted for the hydraulic motor and air accumulator.

In order to pay out or take in cable from the winch 29, it is driven bya fluid motor 41' through a gear reduction box 41. The motor in turn isdriven by a servo controlled fiuid pump 42. As is conventional in suchpumps, the servo or electrical motor 43 of this pump is operative toposition the pump hanger in accordance with an electrical command signalfrom an amplifier 44. The actual position of the pump hanger isreflected by an electrical pct 45 operative to generate an electricalfeedback signal which is returned to the amplifier 4-4 via a feedbacklead 46. The output of the amplifier 44 is thus a ditlerential or errorsignal which is proportional to the difference between the command inputsignal and the feedback signal from the pct 45.

The winch 20 may be operated in either a manual or an automatic mode ofcontrol. In the manual mode, the command signal to the amplifier 44 isderived from the positioning of a manually controlled handle 43operative to generate a signal which varies between -5 and +5 volts. Thepolarity of this signal controls the direction of Winch rotation and theamplitude determines the speed of winch operation. This input signal isfed into the pump control amplifier 4% via an electrical lead 49 througha normally closed contact RC-l of a mode control relay (not shown). Solong as a differential in either polarity or amplitude exists betweenthe command input on the lead it and the feedback. signal on lead 46,the resultant error output from the amplifier 44 continues to repositionthe hanger of the pump 42. When the error is reduced to zero, the hangerposition will be maintained and the speed and direction of rotation ofthe winch drum 24} will be maintained. Thus, in the manual mode ofcontrol, the winch drum 2% simply responds to the speed and directioncommand of the handle position. In the normal course of events, themanual control mode is used only during rigging of the cable between theships. As soon as the rigging is complete and the highline cable 14extends between and is attached to both ships, the control is switchedto automatic operation by actuation of the control relay (not shown) sothat a tension within a predetermined range is maintained on thehighline.

In the automatic mode of control, the winch 20 maintains a predeterminedaverage ram tensioner position irrespective of all ship movements. Tothis end, it pays out cable whenever the ram tensioners position exceedsa preset value and takes in cable whenever the ram tensioner is relaxedto too great an extent.

Upon actuation of the control relay (not shown) which switches thecontrol from manual to automatic control, the normally closed contactRC4 is opened and a normally open contact RC-Z is closed. This resultsin the command signal to the amplifier 44 being derived from atransducer 53 attached to the ram 21 rather than from manual control ofthe handle 43. This transducer is operative to convert linear movementof the movable pulley 3.. into an electrical command signal. To this endthe transducer comprises a mechanical arm indicated by a dashed line 52.in FIGURE 2, connected. to a wiper arm 74 of a potentiometer 75'operative to generate a position feedback signal of, varying amplitudewhenever the position of the ram tensioner is different from the presentvalue. If the tension in the cable 14 is relaxed, the pulley 32 movesaway from the fixed pulley 31 with the result that the transducer 53generates a positive voltage signal in a lead 56. Alternatively, if thetension in the cable exceeds the preset value, the pulley 32 is movedtoward the fixed pulley 31 with the result that a negative polaritysignal is generated in the lead 56.

The signal in lead 56 serves as an input to three parallel circuits tothe command amplifier 44. These three circuits comprise a signalduration damping circuit, a position override control circuit, and aposition rate of change override control circuit.

The signal duration damping circuit functions to dampen out any signalwhich has not persisted for a preset time interval, preferably aboutone-half the normal roll cycle time of the supply ship. in this way, thewinch is precluded from rhythmically operating to pay out or take inline with each roll cycle.

The ram 21 has approximately feet of capacity and is capable ofcompensating for the roll of the two ships. Therefore, the signalduration damping circuit is included to avoid operation of the winch tocompensate for errors which can be handled by the ram tensioner.

The position override control circuit functions as a safety circuitwhich operates the winch whenever the tension in the cable moves the ramtensioner outside a predetermined safety range, irrespective of theduration of the signal. In other words, this circuit operates toimmediately initiate operation of the winch whenever the position of theram tensioner goes beyond a safe operating range.

The position rate of change override control circuit similarly functionsas a safety valve. It operates to im- .ediately initiate operation ofthe winch whenever it detects that the tension in the cable is changingat a rate which, if allowed to continue, would result in damage to theequipment.

In order to eliminate hunting or constant operation and reversing of thedrive to the winch drum, the command signal from the transducer 53 isfirst fed through a tension amplitude discriminating circuit whichcomprises a pair of Zener diodes 57 operative to pass only signals whichexceed plus or minus two volts. In other words, these Zener diodes blockany signals in the range between +2 and -2 volts.

The signal duration damping circuit is essentially a ramp generatorcircuit. This ramp generator circuit 60 (enclosed by the dashed box 60a)comprises a high gain amplifier circuit 61 (enclosed by the dashed box61a), a signal clamping circuit 62 (enclosed by the dashed box 62a), andan integrating circuit '63 (enclosed in the dashed box 63a). Amplifiercircuit 61 is a conventional high gain amplifier operative to amplifyany signal within the range of at least volts. The output from thisamplifier is fed through the conventional clamping circuit 62 comprisinga pair of Zener diodes 64, 65 connected in series. These Zener diodesclamp any signal of more than +6 volts or less than '6 volts. The outputfrom this clamping circuit 62 is fed via lead 66 as an input into theconventional integrating circuit 63. The integrating circuit 63comprises a conventional amplifier having a high capacitance feedbackloop. The output of this integrating circuit 63 is fed as an input vialead 59 into an amplitude discriminating circuit 6*? and as a negativefeedback signal via lead 73 back to the high gain amplifier circuit 61.Amplifier 61 clamps at :6 volts with a difference of :M; volts betweenleads 58 and 73. The discriminating circuit 67, which comprises a pairof series connected Zener diodes 68, 69, is operative to pass onlysignals outside a predetermined range, as for example, signals greaterthan +2 volts and less than 2 volts. From the discriminating circuit 67,the output signal is fed as an input into the pump command amplifier 44.

Referring now to FIGURE 3, there is represented graphically, on adistance versus time plot, the roll of the supply ship. As depicted bythe dotted line 70, the roll normally varies from a center position to adistance of-approxirnately 30 feet and occurs during a time interval ofseconds. In other words, the supply ship rolls from one extreme positionto an opposite extreme position during approximately 7 /2 seconds.Superimposed on the same graph, is a plot 71 (depicted by a solid line)of a voltage versus time of the input signal to the integrating circuit63. As may be seen in this graph, the input signal from the high gainamplifier 61 quickly builds up to a value of 6 volts and holds at thisvalue as a consequence of being clamped by the clamping circuit 62. Theout-put of the integrating circuit 63 is depicted by a dashed line 72 inFIGURE 3. As may be seen in this figure, the output is a ramp whichslowly builds to a value of 2 volts after a time interval of 7 /2seconds.

When the output signal of the integrating circuit 63 builds to the valueof more than +2 volts or less than 2 volts, it is passed by the Zenerdiodes 68, 69 into the control amplifier 44.

The net effect of the ramp generator circuit 60 is to dampen out anyfeedback signal which has persisted for a time interval of less than 7/2 seconds, one-half the normal roll cycle time of the supply ship. Ifthe signal continues to build after 7 /2 seconds, as it does when theships are on diverging courses, the output signal from the rampgenerator builds to more than 2 volts and then is passed by the Zenerdiodes 68, 69 as an input into the control amplifier so as to result inoperation of the winch.

The position override circuit 78 comprises a pair of Zener diodes 80, 81connected in series in a circuit which parallels the ramp generator.These Zener diodes 80, 81 receive as an input the signal in lead 58 andoperate to block any signal of less than predetermined amplitude, as forexample, any signal in the range between +4 volts and 4 volts. Anysignal passed by the Zener diodes S0, 81 serves as an input to aconventional amplifier 82, the output of which is fed via lead 83 as acommand signal to the amplifier 44.

Any signal passed by the Zener diodes 80, 81 is an indication of a veryhigh or very loW position of the ram tensioner. Consequently, the gainof amplifier 82 is sufficiently high to cause the pump 42 to go on fullstroke or, otherwise expressed, to operate the winch at its maximumoperating speed.

The operation of the position override control circuit 78 is depictedgraphically in FIGURE 5. In this graph, the position of the ramtensioner which results from normal roll of the two ships is depicted bysolid line 92. In the normal course of events, and assuming that the twoships are on parallel courses, the ram tensioner would never move asuflicient distance from the zero center line position to generate aposition override signal greater than +4 volts or less than -4. However,it as depicted by the dashed line 93, the two ships converge asufficient distance to enable the ram tensioner to move to a positionwhich results in the generation of a signal of less than 6 volts, theline will go slack. Alternatively, if the ships part sutficiently togive rise to a ram tensioner position signal of more than +6 volts, theline will part or break. Before either of these alternatives occur, andas depicted by the dashed line 94, the position override control circuit'78 passes a signal through the Zener diodes 80, 81 to the amplifier 82Which results in the pump 42 going on full stroke to operate the Winchto take in cable if the the value of the signal is less than +4 volts orto pay out cable if the value is more than +4 volts.

The position rate of change override control circuit 86 has the sameeffect of causing the pump 42 to go on full stroke whenever it detectsthat the position of the ram tensioner is changing at an excessivelyhigh rate. This circuit 86 comprises a conventional R-C circuit whichreceives as its input, the output of the ram tensioner feedbackpotentiometer 53 via lead 56. The output of the RC circuit 86 is fed asan input to an amplitude discriminating circuit comprising a pair ofdiodes 89, 9t) operative to pass only signals above a predeterminedamplitude, as for example, +1 or 1 volt. Any signal passed by thesediodes becomes an input to the amplifier -82 via a lead 91 and afterbeing amplified, is fed as an input to the control amplifier 44 via lead83.

FIGURE 4 illustrates graphically the operation of the position rate ofchange control circuit 86. So long as the slope of the line 95representing movement of the ram tensioner resulting from ship roll doesnot exceed a predetermined value, there is no resulting signal passed bythe R-C circuit -86. However, if the rate of movement of the ramtensioner suddenly changes, as depicted by the dashed line 96, the slopeof the line changes and the R-C circuit passes a command signal to theamplifier 82, which results in the operation of the winch. Thus thiscircuit causes the winch to be immediately operative before the line cango slack or can be tensioned to the breaking point. As depicted inFIGURE 4, the winch is caused to operate and take in line before theline can go slack so that the corrected movement of the ram tensionerfollows the dashed line 97 rather than line 96. It is to be noted thatthis correction is initiated by the rate of change control circuit 86even before the ram tensioner passes through the zero or centeredreference position so that the potential slack condition is detectedvery early and corrected before slack can develop.

In operation, the automatic control circuit is operative to measure theposition of the ram tensioner and, if it exceeds a predetermined range,to command operation of the winch through one of the three parallelcontrol circuits. The time damping circuit only passes a signal whichpersists for a time interval of 7 /2 seconds or more so that it averagesout the normal position changes resulting from the roll of the twoships. If a signal persists for more than 7 seconds, indicating that theships are on a relatively converging or diverging course, this dampingcircuit passes a command signal to the control amplifier 44 causingcompensatory movement of the winch drum to pay out or take in cable asrequired to bring the ram tensioner back into the preset range.

If the position of the ram tensioner goes beyond the safe operatingrange, the output of the transducer will be of such magnitude as to bepassed by the Zener diodes 80, 81 and 57 as an input to the amplifier82, and from the amplifier 82, as a command to the amplifier 44. Thisposition override signal then causes the pump to go up to full strokeand operate the winch up to rated speed until the measured position isback in the safe operating range.

Similarly, if the position rate of change measuring circuit 86 detectsthat the position is changing at a very high rate, the RC circuit willfeed an input through the diodes 89, 90 as an input into the amplifier82. The output of this amplifier is then fed as an input into thecontrol amplifier 44 which also causes the winch to operate at speeds upto maximum speed until the rate of speed at which the position ischanging is brought back into a safe range.

While only a single preferred embodiment of this invention has beendisclosed and described herein, those skilled in the arts to which thisinvention pertains will readily appreciate numerous changes andmodifications which may be made without departing from the spirit of ourinvention. Specifically, those skilled in this art will appreciate thatthere are hydraulic and mechanical equivalents of the electrical controlcircuits described hereinabove and that these equivalents may besubstituted for the electrical controls to achieve the same results.Therefore, we do not intend to be limited except by the scope of theappended claims.

Having described our invention, we claim:

1. A control system for maintaining a preset tension upon a cableextending between two moving ships at sea, said cable extending from awinch drum on one ship, through a ram tensioner on the same ship, andover to the other ship,

said ram tensioner comprising a pair of spaced, multiple wrap pulleysover which said cable extends, said pulleys being mounted for movementrelative to each other and being biased apart by a compressible element,

transducer means for generating an electrical signal having acharacteristic which is a function of said compression and thus of theposition of said ram tensioner,

an electrical control circuit having said electrical signal from saidtransducer as an input,

means including said electrical control circuit for operating said Winchso as to maintain a predetermined range of said rarn tensioner position,and

said control circuit including control means operative to dampen outshort time duration position feedback signals so that said winchoperating means only responds to a position feedback signal within apredetermined range after it has persisted for a predetermined timeinterval.

2. The control system of claim '1 which further includes a positionoverride control circuit by-passing said control means to actuate saidwinch, operating means upon meas urement of a position of said ramtensioner above said predetermined range such that said winch operatingmeans is responsive to a position change above said predetermined rangeirrespective of the time interval during which it is maintained.

3. The control system of claim 1 which further includes a position rateof change control circuit by-passing said control means to actuate saidwinch operating means in the event of a rapid position change of saidram tensioner so that said winch responds to a high rate of change ofposition or said ram tensioner irrespective of the time interval duringwhich it occurs.

4. The control system of claim 1 wherein said predetermined timeinterval is at least equal to one-fourth the normal roll cycle time ofsaid one ship but not more than the duration of a complete roll cyclefor said ship.

5. A control system for maintaining a preset tension upon a cableextending between two moving ships at sea, said cable extending from awinch drum on one ship, through a ram tensioner on the same ship, andover to the other ship,

said ram tensioner comprising a pair of spaced multiple wrap pulleysover which said cable extends, said pulleys being mounted for movementrelative to each other and being biased apart by a compressible element,

transducer means for generating an electrical signal having acharacteristic which is a function of the position of the ram tensioner,

an electrical control circuit having said electrical signal irom saidtransducer as an input,

means including said electrical control circuit for controlling a servocontrolled fluid pump, said pump being operative to drive a fluid motorwhich in turn drives said winch drum, said control circuit beingoperative to maintain the tension in the cable within an acceptablerange, and

said control circuit including a ramp generator circuit in series withan amplitude discriminating circuit operative to dampen out largeamplitude, short time duration, position feedback signals so that saidwinch operating means only responds to a position feedback signal withina predetermined range after it has persisted for a predetermined timeinterval.

6. The control system of claim 5 which further includes a positionoverride control circuit by-passing said ramp generator circuit, saidposition override circuit comprising an amplitude discriminator circuitoperative to actuate said servo controlled pump in response to aposition feedback command above said predetermined range irrespective ofthe time interval during which it is maintained.

7. The control system of claim 5 which further includes a position rateof change control circuit by-passing said ramp generator operative toactuate said servo controlled pump in the event of a rapid positionchange in said ram tensioner so that said winch responds to a high rateof change of position in said ram tensioner irrespective of the timeinterval during which it occurs.

8. The control system of claim 5 wherein said prede termined timeinterval is at least three seconds but not more than the duration of anormal roll cycle for said one ship.

9. The method of maintaining a preset tension upon a cable extendingbetween two moving ships at sea, which cable extends from a winch drumon one ship, through a ram tensioner on the same ship, and over to theother ship, said ram tensioner having a pair of spaced, multiple wrappulleys mounted for movement relative to each other and biased apart bya compressible element, which method comprises generating an electricalsignal having a characteristic which is a function of the position ofthe ram tensioner,

using said characteristic of said electrical signal to control saidwinch drum so as to maintain a predetermined range of tension in saidcable, and

damping short duration characteristic changes in said electrical signalso that said winch responds only to a position feedback signal within apredetermined range after it has persisted for a predetermined timeinterval which is at least as long as one-fourth the characteristic rollcycle time of said one ship.

10. The method of claim 9 which further includes the step of utilizingsaid electrical command signal to oper- Q 10 ate said winch at any timesaid position feedback signal References Cited exceeds saidpredetermined range such that said Winch is UNITED STATES PATENTSresponsive to a position above said predetermined range irrespective ofthe time interval during which it is main- 3,150,860 10/1964 Nelson254-172 tamed. 5 3,309,065 3/1967 PrudHomme 254-472 @3331; $3 iiiiiifnial i ii nii ii i 222?? iii? FOREIGN PATENTS P g p 315,176 2/1934Italy.

winch drum at any time said signal exceeds a preset rate of change sothat said winch responds to a high rate of change of position of saidram tensioner irrespective of 10 EVON BLUNK P'lmary Exalmner' the timeinterval during which it occurs. H. C. HORNSBY, Assistant Examin

